Blasting operations frequently trigger a series of explosions in an exact order, with precise timing. For this purpose, blasting systems have been developed that employ shock tubes (also known as signal transmission lines) that transfer a blast initiation signal to an explosive charge. A signal from a single shock tube can be transferred to multiple shock tubes in a blasting system via the use of connector block/detonator assemblies, thereby permitting the initiation of multiple explosive charges in a controlled manner.
Safety and reliability are paramount for any blasting system, and efficient shock tube initiation is an important factor in this regard. Shock tubes that fail to initiate result in unexploded charges at the blast site, with inevitable safety concerns. Moreover, the reliable initiation of shock tubes is imperative to ensure that the required blasting pattern is effected.
The efficiency of shock tube initiation is dependent primarily upon connector block design. Reliable initiation of shock tubes requires the transfer of sufficient energy from the base charge of the detonator to the shock tubes, thereby compressing the shock tubes rapidly with sufficient energy and speed to initiate them.
The shock tube retention means of a connector block holds one or more shock tubes in contact with, or close proximity to, the percussion-actuation end of the detonator retained within the block. Importantly, the shock tube retention means ensures that the shock tubes are retained in signal transmission relationship with the detonator. Several examples of connector block designs are known in the art, which comprise a shock tube retention means for holding at least one shock tube adjacent to the percussion-actuation end of the detonator. These examples generally encompass the use of a flexible clip-like member, integral to the connector block, for retaining the shock tubes within a slot formed between the clip-like member and the percussion-actuation end of the detonator. In this way, the shock tubes are retained in signal transmission relationship with the end of the detonator.
In one example, U.S. Pat. No. 5,204,492, issued to ICI Explosives USA Inc. on Apr. 20, 1993, discloses a detonator assembly for initiating up to eight transmission lines. The assembly comprises a connector block that houses a low strength detonator by means of a confining wall surrounding the closed end of the low strength detonator. One or more signal transmission lines can be inserted through a gap in the confining wall and operatively confined adjacent to the closed end of the low strength detonator.
U.S. Pat. Nos. 5,171,935 and 5,398,611, issued to the Ensign Bickford Company on Dec. 15, 1992 and Mar. 21, 1995 respectively, disclose a connector block having a housing with a channel formed therein for receiving a low energy detonator. The connector block further comprises a shock tube engaging member for holding shock tubes (referred to as transmission tubes) adjacent an end of the channel, wherein the tube engaging member is attached to the connector block via a resiliently deformable segment. Shock tubes may be inserted into a slot formed between the housing and the tube engaging member.
U.S. Pat. No. 5,499,581 issued to the Ensign-Bickford Company on Mar. 19, 1996, discloses a connector block design for connecting signal transmission lines in a blasting system. The patent discloses improved means for securing a detonator within the connector block via a displaceable locking member. The connector block may further comprise a flexible, cantilevered line retaining means to receive one or a plurality of outgoing signal transmission lines.
In another example, U.S. Pat. No. 5,703,319, issued to the Ensign Bickford Company on Dec. 30, 1997, discloses a connector block comprising a clip member. The clip member cooperates with the signal transmission end of a body member to define a slot for receiving one or more signal transmission lines in communication with the output end of a detonator. The clip member is characterised in that it comprises a section of continuously reducing thickness to facilitate lateral insertion of signal transmission lines into the slot by deformation of the clip member.
In another example, U.S. Pat. No. 5,659,149 issued to the Ensign Bickford Company on Aug. 19, 1997 discloses connector blocks comprising a slot for retaining a single acceptor line in an undulate configuration therein (i.e. the single acceptor line is contorted to have multiple bends or kinks). In a preferred embodiment, the connector blocks may further include a moveable retainer member located on a side of the slot opposite the detonator end. The moveable retainer member is generally integral with the shock tube retention means, and includes a barb for retaining the single acceptor line in position adjacent the end of a detonator.
In a final example, the so called Handidet™ X405 provides for a connector block for retaining shock tubes in signal transmission relationship with the percussion-actuation end of a detonator. The shock tubes are retained in a slot defined between a flexible shock tube retention means and the adjacent housing of the connector block. The entrance to the slot is formed between a semi-rigid member integral with the housing, and a flexible tip integral with the flexible shock tube retention means. Shock tubes may be inserted through the entrance of the slot by deformation of the flexible shock tube retention means (and, in particular, the flexible tip), and the semi-rigid member integral with the housing. Importantly, the access to the slot depends primarily upon the flexibility of the shock tube retention means and the flexible tip. Although the semi-rigid member exhibits a limited degree of flexibility, the principle function of this member is to retain the shock tubes within the connector block once inserted into the slot.
The connector blocks disclosed in the prior art generally comprise shock tube retention means comprising a material with a significant degree of resilient flexibility. The flexibility of the shock tube retention means permits facile insertion of the shock tubes between the shock tube retention means and the percussion-actuation end of a detonator housed within the block. For this purpose, the shock tube retention means comprises a member that can be temporarily deformed by application of force by the user, thereby allowing access to a slot (or equivalent thereof) for insertion of the shock tubes therein. Release of the force permits the shock tube retention means to assume its original configuration, and retain the shock tubes in the slot.
A variation on this theme is provided by U.S. Pat. No. 5,659,149 (as previously described), in which a single acceptor line is retained by a resilient barbed member generally integral with the shock tube retention means. Nonetheless, the configuration of the disclosed connector blocks is such that only a single line may be retained, and the shock tube retention means comprises complex components that reduce the integrity of the connector block upon detonator initiation, thereby increasing the quantity of shrapnel.